The present invention relates to a method of moulding a composite article and mould.
There are a variety of composite manufacturing processes which each have advantages and disadvantages. The factors which drive selection of the process include structural quality of the part, cost, surface finish, production rate, volume and limitations of the method. Common composite manufacturing methods are hand lay-up, pre-preg lay-up, bag moulding, autoclave processing, compression moulding, resin transfer moulding, pultrusion and filament winding. The two methods that are most appropriate for comparison to the invention are both resin transfer moulding (RTM) processes. The two methods are conventional RTM and vacuum assisted RTM (VARTM).
Resin transfer moulding (RTM) involves using a closed mould with two rigid surfaces. Fibre reinforcement is placed in the mould which is then closed. Liquid resin is then injected into the mould to wet out the reinforcement and fill the mould cavity. The resin supply is then removed and heat is applied to cure the composite part. By using a mould with two rigid surfaces, a high quality finish of both sides of the moulded article is achieved. This process can produce large, complicated shapes and relatively short cycle times. However, this remains a relatively expensive process as the cost of the equipment to inject the resin under high pressure is high as is the cost of the tooling which can safely contain such pressure.
Vacuum assisted resin transfer moulding (VARTM) involves the application of a vacuum to draw resin into the mould. As the resin is infused via a vacuum, half of the mould can be replaced by a vacuum bag. The pressure differential is much lower than in conventional RTM so the cost of the mould can be lower. For example, heavy steel moulds can be replaced by lightweight moulds. The VARTM process can produce one high quality surface against the rigid mould surface. However, the opposite surface which is produced by the surface of the vacuum bag cannot be precisely defined given the distortions of the vacuum bag particularly in the vicinity of any well-defined corners. This process also requires a relatively large number of consumable parts including the vacuum bag, the distribution mesh and the sealant tape required to seal the edge of the vacuum bag.